Catalytic Chain Transfer Research Articles

Subtle effects control the polymerisation mechanism in α-diimine iron catalysts

α-diimine iron complexes have been suggested to catalyse polymerisation via two distinct pathways, depending on the spin state of the iron complex. Here, we study a typical complex of this family, (R'')[N,N]FeCl(2), with [N,N] = Cy-N=CR''-CR''=N-Cy (Cy = cyclohexyl, R'' = PhF (para-fluorophenyl), PhOMe (para-methoxyphenyl), PhNMe(2) (para-dimethylaminophenyl). With R'' = PhF, PhOMe, polymerisation proceeds as a catalytic chain transfer (CCT) mechanism, with R'' = PhNMe(2), the polymerisation follows an atom transfer radical polymerisation (ATRP) pathway. Contrary to previous suggestions, we show that the spin-states of the complexes involved are not affected by the R'' group. Instead, the different behaviour arises from a subtle interplay between the electron-withdrawing or donating character of the reasonably distant phenyl substituent and the iron centre, and small but crucial differences in the reorganisation energies affected during the reactions.

Mass transport by collisions in emulsion polymerization: why it is possible to use very hydrophobic catalysts for efficient molecular weight control

An alternative mass transport mechanism, based on collisions between different entities, is used to explain the performance of an extremely hydrophobic catalytic chain transfer agent (i.e.COPhBF) in emulsion polymerization. Mass transport in emulsion polymerization is generally accepted to proceed via the aqueous phase. COPhBF possesses no detectable water-solubility and would therefore be expected to be inefficient for molecular weight control in emulsion polymerization. However, proper molecular weight control using COPhBF has been demonstrated and results are presented that are consistent with the existence of an alternative mass transport mechanism in emulsion polymerization that circumvents the aqueous phase.

Porphyrins and Their Metal Complexes in Radical Polymerization of Vinyl Monomers

Recently, controlled radical polymerization has become one of the most important methods for producing synthetic vinyl polymers. At the moment several techniques enabling such polymerizations exist, of which ATRP (atom transfer radical polymerization) and RATRP (reverse atom transfer radical polymerization) are the most commonly used ones. [1] The significant advantages of these polymerization techniques include the ability to polymerize polymers with controlled density and chain length, and narrow molecular weight distribution (MWD) in a controlled manner. A wide range of compounds as alkoxyamines, dithioesters, trithiocarbonates, xanthates and others were proposed as propagation regulators. Metalloorganic compounds of general formula MtnYL, where Mt transition metal (Cu, Fe, Ru, Re, Ni and others); Y – halogen anion (mainly chlorine or bromine); L – organic ligand (mostly 2,2’-bipyridine, 4,4’-bi-(5-nonyl)-2,2’-pyridine, triphenylphosphine) are of great interests also. The use of metal complexes of porphyrins in controlled radical polymerization could be very promising.[2-6] Thus, catalytic chain transfer to the monomer and catalytic inhibition were discovered in the polymerization of methacrylates carried out in the presence of cobalt porphyrins.[2-5] It was found by B.B. Wayland and M. Fryd that cobalt complex of tetramesitylporphyrin initiates polymerization of acrylates leading to the formation of homopolymers and block copolymers.[7-9] However, only few metal porphyrins, which are well-soluble in organic media, mainly, cobalt, rhodium, aluminum complexes, allowing the radical polymerization of vinyl monomers under controlled mode, have been studied by now.[7-11] The goal of this work was the study of radical polymerization of vinyl monomers (by the example of methyl methacrylate (MMA) and styrene) initiated by azo-bis-isobutironitrile (AIBN) or benzoyl peroxide (BP) in the presence of various porphyrins and their metal complexes.

Combining catalytic chain transfer polymerisation (CCTP) and thio-Michael addition: enabling the synthesis of peripherally functionalised branched polymers

Catalytic chain transfer polymerisation (CCTP) of divinyl monomers has been used to synthesise a family of branched polymers, which retain vinyl functionality; a range of decorated branched polymers have been prepared via thio-Michael addition.

Synthesis and modification of thermoresponsive poly(oligo(ethylene glycol) methacrylate) via catalytic chain transfer polymerization and thiol–ene Michael addition

Various poly(oligo(ethylene glycol) methyl ether methacrylate)s (POEGMEMAs) have been prepared by Catalytic Chain Transfer Polymerization (CCTP) using a range of OEGMEMA monomers (molecular weight from 180 to 1100 g mol−1). The chain transfer constants of bis(boron difluorodimethylglyoximate) cobalt(II) (CoBF) were determined and are reported for each monomer. The copolymerization of POEGMEMA (Mn = 475 g mol−1) with diethylene glycol methyl ether methacrylate (DEGMEMA) yielded thermoresponsive polymers. The lower critical solution temperatures (LCSTs) of the polymer chains can be tuned by the copolymer composition over the range 30 °C to 95 °C. In addition, the presence of the vinylic end-group, characteristic of CCT polymerization, provided further scope for post-synthetic modification via thiol–ene click chemistry, through nucleophilic Michael addition with various functional thiol compounds such as 2-mercaptoethanol, 3-mercaptopropionic acid, benzyl mercaptan and 1-dodecanethiol. The thiol–ene reaction was rigorously tested, optimized and characterized in this study in terms of solvents and most importantly the choice of the catalyst: dimethyl phenyl phosphine, tertiary amine or hexylamine. The optimum conditions reported allow near-quantitative functionalization of these macromonomers without significant side reactions. The effect of the end-group on the LCST has also been investigated, as well as thermal stability temperature of the copolymers.

A New Method for the Preparation of Concentrated Translucent Polymer Nanolatexes from Emulsion Polymerization

A novel method for the preparation of concentrated, colloidally stable, translucent polymer nanolatexes is presented. Herein nanolatexes are obtained from emulsion polymerization, utilizing the potential of catalytic chain transfer to enhance the particle nucleation efficiency. Low amounts of emulsifier are required (<8% w/w based on monomer) while the nanolatexes concentration can be increased to 40% w/w. The nanolatexes are translucent in appearance, which was correlated to the average particle size and width of the particle size distribution using Mie theory. Increasing the nanolatex concentration was found to have no deteriorating effect on either the optical or colloidal properties. Preparing translucent nanolatexes via this method is advantageous, as the amount of emulsifier is significantly reduced without sacrificing the optical transparency or the high interfacial surface area of the polymer colloids.

Graft polymers prepared by catalytic chain transfer polymerization (CCTP) and applied as solvent-borne dispersants for carbon black dispersions of high solid

AbstractIn this article, a series of graft polymer dispersants were conveniently prepared by the grafting through method, among which the macromonomer was synthesized with one-pot through CCTP technology. Rheology and transmission electron microscopy (TEM) were utilized to study the influence of amide content on the carbon black (CB) dispersing ability of these polymers in xylene. When the tertiary amino groups on the backbone were partly quaternized, the apparent viscosity of the obtained CB suspensions decreased remarkably and the flocculation of the CB particles are effectively suppressed. TEM observations showed that the CB particles were well dispersed by the quaternized dispersant. It could be concluded that the graft polymers with a certain amount of quaternized amino groups (20 wt.%) are an efficient dispersants of CB in organic solvent.

Catalytic Chain Transfer Mediated Emulsion Polymerization: Compartmentalization and Its Effects on the Molecular Weight Distribution

We present the first population balance calculations which encompass the complete molecular weight distribution (MWD) to discuss the implications of both radical and catalytic chain transfer agent (CCTA) compartmentalization in a catalytic chain transfer (CCT) mediated emulsion polymerization system. Compartmentalization effects are attributed to reduced frequencies of entry and exit of the CCTA (bis[(difluoroboryl)dimethylglyoximato]cobalt(II) or COBF). Two limiting scenarios were identified. In instances of fast CCTA entry and exit, monomodal MWDs are obtained governed by a global CCTA concentration. In instances of slow entry and exit, bimodal MWDs are obtained; one peak can be attributed to the generation of a bimolecular termination product produced in polymer particles devoid of CCTA, while a transfer-derived peak can be attributed to polymer particles containing one or more CCTA molecules. We present theoretical evidence that experimentally observed multimodal MWDs (Macromolecules 2009, 42, 7332−7341) originate from a reduced mobility of the CCTA and that when viscosity is high in the polymer particles, compartmentalization of the CCTA becomes important.

Controllable Fabrication of Nanocrystal-Loaded Photonic Crystals with a Polymerizable Macromonomer via the CCTP Technique

We report an alternative strategy for fabricating nanocrystal-loaded photonic crystals with a polymerizable macromonomer via catalytic chain-transfer polymerization (CCTP) in which CoBF acted as a chain-transfer agent (CTAs). First, monodisperse, functionalized PS-co-PMAA microspheres with polystyrene (PS) cores and poly(methacrylic acid) (PMAA) shells were controllably prepared using styrene and the as-prepared PMAA macromonomer by surfactant-free emulsion polymerization. Then Cd(0.4)Zn(0.6)S nanocrystals capped with as-prepared PMAA macromonomer were synthesized by an in situ growth method. Finally, Cd(0.4)Zn(0.6)S nanocrystal-loaded PS-co-PMAA microspheres hybrids were obtained through simply mixing an aqueous solution of PS-co-PMAA microspheres with an aqueous solution of Cd(0.4)Zn(0.6)S nanocrystals in the appropriate proportions; the multianchor -COOH groups on the surface of core-shell PS-co-PMAA microspheres favor incorporation with Cd(0.4)Zn(0.6)S nanocrystals. Scanning electron microscopy (SEM) images confirm that PS-co-PMAA microspheres are uniformly surrounded by Cd(0.4)Zn(0.6)S nanocrystals. In addition, discrete electronic and photonic states can be combined both with PS-co-PMAA photonic crystals and fluorescent semiconductor Cd(0.4)Zn(0.6)S nanocrystals.

The effect of different catalytic chain transfer agents on particle nucleation and the course of the polymerization in ab initio batch emulsion polymerization of methyl methacrylate

The effect a Co(II) based catalytic chain transfer agent (CCTA) has on the course of the polymerization and the product properties of an emulsion polymerization is governed by the intrinsic activity and the partitioning behavior of the catalyst. The effect on the conversion time history, the molecular weight distribution and the particle size distribution is evaluated in batch emulsion polymerization of methyl methacrylate for three different CCTAs, which cover a range of intrinsic activities and partitioning behaviors. It was demonstrated that radical desorption from the particle phase to the aqueous phase preceded by chain transfer is the main kinetic event controlling the course of the polymerization and the product properties in terms of the particle size distribution. The experimental results show that the aqueous phase solubility of the CCTA is the key parameter controlling the course of the polymerization and the particle size distribution. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1038–1048, 2010

Facile and selective synthesis of aldehyde end-functionalized polymers using a combination of catalytic chain transfer and rhodium catalyzed hydroformylation

A novel synthetic pathway towards aldehyde end-functionalized polymers is presented from a combination of catalytic chain transfer polymerization (CCTP) and rhodium catalyzed hydroformylation in supercritical carbon dioxide. CCTP allows for the synthesis of well-defined macromonomers in terms of the average molecular weight and the terminal unit carrying the unsaturated bond. The rhodium catalyzed hydroformylation allows for a high selectivity towards aldehyde end-group functionalized polymers. The introduction of the synthetically versatile aldehyde end-group opens up a broad range of possible applications.

High fidelity vinyl terminated polymers by combining RAFT and cobalt catalytic chain transfer (CCT) polymerization methods

In this work, we combine reversible addition fragmentation transfer polymerization (RAFT) with cobalt catalytic chain transfer (CCT) to obtain omega-unsaturated polymers with relatively low polydispersity values.

Controllable Synthesis of New Polymerizable Macrosurfactants via CCTP and RAFT Techniques and Investigation of Their Performance in Emulsion Polymerization

We reported herein the synthesis of poly(methacrylic acid)-b-poly(butyl acrylate) (PMAA-b-PBA) block copolymers (surfmers) and their performance as novel polymerizable macrosurfactants in emulsion polymerization. The surfmers bearing terminal unsaturated carbon-carbon double bonds were first successfully designed and sythesized via catalytic chain transfer polymerization (CCTP) and radical addition-fragmentation polymerization (RAFT) techniques. The structures of surfmers were characterized by Raman spectra, nuclear magnetic resonance ((1)H NMR), and gel permeation chromatography (GPC). The critical micelle concentration of surfmers was determined. Subsequently, the surfmers were used as emulsifier to prepare polyacrylate latexes (PA-surf). The influence of the surfmer concentration as well as PMAA and PBA chain segment ratios of surfmer on their performance in emulsion polymerization was discussed thoroughly. The particle size, amount of coagulum, and stability against electrolyte solutions of the latexes were evaluated. Also, the relations between monomer conversion in emulsion polymerization, polymerization rate, emulsion particle size, surface tension, and reaction time were investigated, which showed some interesting information for the probable mechanism underlying this emulsion polymerization system. Atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared spectra (ATR FT-IR) were performed to investigate the surface morphology and component distribution of the latex films. The results show high efficiency of these surfmers in emulsion polymerization, suggesting that the resultant PMAA-b-PBA block copolymers act not only as the emulsifier but also as the stabilizer of monomer droplets as well as the so-called comonomer.

P71 Vascular endothelial growth factor (VEGF) inhibition and erythropoiesis – a missing link?

Herein, we have designed a novel multilayer system composed of poly(methyl methacrylate) [poly(MMA)] brush, biotin, streptavidin and protein-A on a silicon substrate to attach on anti-immunoglobulin G (anti-IgG). poly(MMA) brush with vinyl end-group was first synthesized by the interface-mediated catalytic chain transfer polymerization. The brush was then modified with cysteamine molecules to generate the polymer chains with amine end-group via a thiol-ene click chemistry. The amine end-groups of poly(MMA) chains were also modified with biotin units to ensure selective connection points for streptavidin molecules. Finally, a multilayer system on the silicon substrate was formed by using streptavidin and protein-A molecules, respectively. This multilayer system was employed to attach anti-IgG molecules in a highly oriented manner and provide anti-IgG molecular functional configuration on the multilayer. High reproducibility of the amount of anti-IgG adsorption and homogeneous anti-IgG adsorption layer on the silicon surface could be provided by this multilayer system. The multilayer system with protein A may be opened the door for designing an efficient immunoassay protein chip.

Evidence of Compartmentalization in Catalytic Chain Transfer Mediated Emulsion Polymerization of Methyl Methacrylate

Evidence of compartmentalization of the catalytic chain transfer agent in seeded emulsion polymerization of methyl methacrylate (MMA) is shown experimentally. The addition of bis[(difluoroboryl)dimethylglyoximato]cobalt(II) (COBF) to seed particles swollen below their maximum saturation concentration exhibited multimodal molecular weight distributions (MWD) which are attributed to a statistical distribution of COBF molecules over the polymer particles. The experimental observations suggest that there are two limits for catalytic chain transfer in emulsion polymerization: (i) at the earlier stages of the polymerization where a global COBF concentration governs the MWD and (ii) at the latter stages of the polymerization where a statistical distribution of COBF molecules governs the MWD. To the best of our knowledge, these results are the first to suggest evidence of compartmentalization in catalytic chain transfer mediated emulsion polymerization.

The effect of Co(II)‐mediated catalytic chain transfer on the emulsion polymerization kinetics of methyl methacrylate

AbstractThe effect the catalytic chain transfer agent, bis[(difluoroboryl) dimethylglyoximato] cobalt(II) (COBF), on the course of the ab initio emulsion polymerization of methyl methacrylate, and the product properties in terms of the molecular weight distribution were investigated. The emulsion polymerization kinetics have been studied with varying surfactant, initiator, and COBF concentrations. The experimentally determined average number of radicals per particle strongly depends on the concentration of COBF and proves to be in good agreement with the results of model calculations. The apparent chain transfer constant, determined up to high conversion, is in excellent agreement with the predicted value based on a mathematical model based on COBF partitioning and the Mayo equation. The results of this work enhance the fundamental understanding of the influence a catalytic chain transfer agent has on the course of the emulsion polymerization and the control of the molecular weight distribution. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5078–5089, 2009

Mass Transport Limitations and Their Effect on the Control of the Molecular Weight Distribution in Catalytic Chain Transfer Mediated Emulsion Polymerization

The existence of mass transport limitations in catalytic chain transfer mediated emulsion polymerization of methyl methacrylate (MMA) using bis[(difluoroboryl)dimethylglyoximato]cobalt(II) (COBF) w...

Electronic and Steric Ligand Effects in the Radical Polymerization of Vinyl Acetate Mediated by β‐Ketoiminate Complexes of Cobalt(II)

Complexes Co[OC(Ph)CHC(Me)NAr](2) [Ar=Ph, 1; o,o'-C(6)H(3)Me(2) (Xyl), 2; p-C(6)H(4)CF(3), 3] are tested in the polymerization of vinyl acetate (VAc) initiated by V-70 (0.8 equiv) at 30 degrees C. Polymerization occurs without any notable induction time yielding PVAc with relatively low polydispersity, but with higher than expected M(n) values, which indicates inefficient trapping processes. The apparent polymerization rate constant varies in the order 2>1>3. Controlled polymer growth is also observed when the polymerization is conducted in the presence of a much higher V-70/1 ratio, demonstrating that this system can also function as a transfer agent in a degenerative transfer process. Competition between chain growth and catalyzed chain transfer (CCT) is also observed, the latter prevailing at higher temperatures. Comparison of these results with previous reports on bis(beta-diketonato) complexes allows a separate assessment of ligand electronic and steric effects in the ability to control polymerization.

In situ synthesis of transparent fluorescent ZnS–polymer nanocomposite hybrids through catalytic chain transfer polymerization technique

We report the controllable synthesis of zinc sulfide (ZnS) nanocrystals (NCs)/polymer transparent nanocomposite hybrids in situ based on the catalytic chain transfer polymerization (CCTP) technique. Firstly, a polymeric ligand PMAA [PMAA = poly(acrylic acid)] with controllable low-molecular-weight and a terminal double bond was synthesized through CCTP. Secondly, with the use of this versatile polymeric ligand containing a large number of anchors as the stabilizer, the ZnS NCs were fabricated. Finally, the surface polymeric ligands containing terminal double bonds were copolymerized with methyl methacrylate monomer to form NCs–polymer hybrids through free radical polymerization. The properties of as-prepared ZnS NCs and their nanocomposite hybrids were thoroughly investigated by Fourier transform Raman spectra, Fourier transform infrared spectrum, transmission electron microscope, ultraviolet–visible, photoluminescence, and thermogravimetric analyses measurements. The spectroscopic studies reveal that ZnS–polymer nanocomposite hybrids have good optical properties.

Controllable fabrication of nanocrystal-polymer hybrids via the catalytic chain transfer polymerization process

A facile catalytic chain transfer polymerization (CCTP) technique has been developed to synthesize covalently linked CdS nanocrystal-polymer hybrids with good optical properties. The in situ polymerization of methyl methacrylate (MMA) on the surface of modified CdS nanocrystals (NCs) with diameter of 5 nm via CCTP process yielded CdS-polymethylmethacrylate (PMMA) hybrid nanocomposites; while the incorporation of hydroxyl-coated CdS NCs into poly(methacryloxypropyltrimethoxysilane) (PMPS)-co-PMMA matrices prepared by CCTP afforded CdS-PMPS-co-PMMA hybrid nanocomposites, which were further cross-linked by free radical polymerization to form CdS NC-polymer network. The spectroscopic studies indicate that as-prepared CdS NC-polymer hybrids show good photoluminescence (PL) and the NC-polymer network exhibits highly enhanced PL property with respect to that before cross-linking. Also described are the probable mechanism for the catalytic chain transfer polymerization on the surface of modified nanocrystal and the measurement of chain transfer constants.